foothill high school science department dna & rna gene regulation

Foothill High School Science DepartmentFoothill High School Science Department

DNA & RNADNA & RNA

Gene RegulationGene Regulation



How Does A Cell Know?How Does A Cell Know?

Which Gene To Which Gene To ExpressExpress

&&

Which Gene Should Stay Which Gene Should Stay SilentSilent??



• When a Gene is When a Gene is ExpressedExpressed::– It Is Transcribed Into It Is Transcribed Into

mRNAmRNA

• When a Gene is When a Gene is SilentSilent::– It Is Not TranscribedIt Is Not Transcribed



• Expression Regulated ByExpression Regulated By– PromotersPromoters

• RNA Polymerase Binding SitesRNA Polymerase Binding Sites• Certain DNA Base Pair SequencesCertain DNA Base Pair Sequences

– StartStart && StopStop Base Pair SequencesBase Pair Sequences

– Regulatory SitesRegulatory Sites• DNA Binding ProteinsDNA Binding Proteins• Regulate TranscriptionRegulate Transcription


Prokaryote Gene Regulation:lac Operonlac Operon

Prokaryote Gene Regulation:lac Operonlac Operon

• What is an What is an Operon??• Group of Genes That Operate TogetherGroup of Genes That Operate Together

• For Example:For Example:– E. coliE. coli ferments lactose ferments lactose

• To Do That It Needs Three Enzymes To Do That It Needs Three Enzymes (Proteins), It Makes Them All At Once!(Proteins), It Makes Them All At Once!

– 3 Genes Turned On & Off Together. This is 3 Genes Turned On & Off Together. This is

known as theknown as the lac Operon (lactose Operon)


Gene Regulation: lac OperonGene Regulation: lac Operon

TheThe laclac Operon Operon– Regulates Lactose MetabolismRegulates Lactose Metabolism– It Turns On Only When It Turns On Only When Lactose Is Present Lactose Is Present &&

Glucose is AbsentGlucose is Absent.

Lactose is a Lactose is a DisaccharideDisaccharide– A Combination of Galactose & Glucose A Combination of Galactose & Glucose

To Ferment Lactose To Ferment Lactose E. coliE. coli Must: Must:1.1. Transport Lactose Across Cell MembraneTransport Lactose Across Cell Membrane

2.2. Separate The Two SugarsSeparate The Two Sugars



Each Task Requires A Specific ProteinEach Task Requires A Specific Proteinbutbut

Proteins Not Needed If Glucose Present Proteins Not Needed If Glucose Present (why waste energy if you already have food?)(why waste energy if you already have food?)

sosoGenes Coding For Proteins Expressed Genes Coding For Proteins Expressed

Only When There Is Only When There Is No Glucose Present But Present But Lactose Is PresentLactose Is Present



= Lactose

ADDADD LACTOSELACTOSE



Key ConceptKey Concept:

TheThe laclac Genes Genes Are:Are:Turned Off Turned Off By RepressorsBy Repressors

AndAnd

Turned On Turned On By The Presence By The Presence Of LactoseOf Lactose


lac Gene Expressionlac Gene Expression

• Operon Has 2 Operon Has 2 Regulatory Regulatory RegionsRegions– PromoterPromoter (RNA (RNA

Polymerase Polymerase Binding)Binding)

– OperatorOperator (O (O region) Bound To region) Bound To A A lac Repressorlac Repressor



• laclac Repressor Repressor– When Bound To When Bound To O O

RegionRegion : Prevents : Prevents Binding of RNA Binding of RNA Polymerase To Polymerase To PromoterPromoter

– Turns The Turns The OperonOperon ““OFFOFF””



• lac Repressorlac Repressor Also Also Binds To LactoseBinds To Lactose– Higher Affinity For Higher Affinity For

LactoseLactose• When Lactose PresentWhen Lactose Present

lac Repressorlac Repressor Is Is Released From Released From O O RegionRegion– Allows Transcription Allows Transcription

of All Three Genesof All Three Genes


Regulation Can Be:Regulation Can Be:

1.1. Based On RepressorsBased On Repressors

2.2. Based On EnhancersBased On Enhancers

3.3. Regulated At Protein SynthesisRegulated At Protein Synthesis


Eukaryotic Gene RegulationEukaryotic Gene Regulation

Operons UsuallyNOT Found In Eukaryotes

Key Concept:Most Eukaryotic Genes Are Controlled

Individually And Have Regulatory Sequences That Are Much More Complex Than Prokaryotic Gene Regulation



• TATA Box– About 30 Base Pairs Long

– Found Before Most Genes

– Positions RNA Polymerase

– Usually TATATA or TATAAA– Promoters Usually Occur Just Before

The TATA Box


Eukaryotic PromotersEukaryotic Promoters

Enhancer SequencesEnhancer Sequences– Series of Short DNA SequencesSeries of Short DNA Sequences– Many TypesMany Types

Enormous Number Of Proteins Can Bind Enormous Number Of Proteins Can Bind To Enhancer SequencesTo Enhancer Sequences

– Makes Eukaryote Enhancement Very Makes Eukaryote Enhancement Very ComplexComplex


Eukaryotic PromotorsEukaryotic Promotors

• Some Enhance Transcription By Some Enhance Transcription By Opening Up Packed ChromatinOpening Up Packed Chromatin

• Others Attract RNA PolymeraseOthers Attract RNA Polymerase

• Some Block Access To GenesSome Block Access To Genes

• Key To Cell SpecializationKey To Cell Specialization– All Cells Have Same ChromosomesAll Cells Have Same Chromosomes– Some Liver, Skin, Muscle, etc.Some Liver, Skin, Muscle, etc.


Regulation & DevelopmentRegulation & Development

• hox Geneshox Genes– Control Organ & Tissue Development Control Organ & Tissue Development

In The EmbryoIn The Embryo

– Mutations Lead To Major ChangesMutations Lead To Major Changes• Drosophila With Legs In Place of Drosophila With Legs In Place of

AntennaeAntennae



hox Geneshox Genes Present In All EukaryotesPresent In All Eukaryotes– Shows Common AncestryShows Common Ancestry

–Pax 6 hox genePax 6 hox gene• Controls eye growth in Drosophila, Mice Controls eye growth in Drosophila, Mice

& Man& Man

• Pax 6Pax 6 from Mouse Placed In Knee from Mouse Placed In Knee Development Sequence Of Drosophila Development Sequence Of Drosophila Developed Into Eye Tissue.Developed Into Eye Tissue.

Common Ancestor >600M Years AgoCommon Ancestor >600M Years Ago

foothill high school science department dna & rna gene regulation

Documents

lac operon slide

lac repressor slide

lac genes

present slide

presence of lactose

transcribed slide

sugars slide

lactose addlactose